1. Field of the Invention
This invention relates to a dielectric filter to be suitably used for a duplexer of a wireless telecommunication apparatus such as a car telephone.
2. Prior Art
An existing dielectric filter of this type typically has a configuration as illustrated in FIG. 14 of the accompanying drawings. A pair of through bores 23a, 23b with a circular cross section are formed running from a face 21a to the opposite face of a rectangularly parallelepipedic block 21 of a dielectric material, whose faces except the face 21a having two of the openings of the through bores 23a, 23b are covered by an external electrode 25, while a pair of internal electrodes 24a, 24b are arranged respectively on the inner peripheral surfaces of the through bores 23a, 23b. Patterned capacitor electrodes 26a through 26d are formed on said face 21a, of which a pair of patterned capacitor electrodes 26a, 26b are respectively connected with the inner electrodes 24a, while the other pair of patterned capacitor electrodes 26c, 26d form input and output terminals.
Reference numeral 10 denotes a substrate to which a dielectric filter as described above is fitted. Such a substrate 10 comprises a patterned grounding electrode 11 to be connected with the outer electrode 25 and patterned input and output electrodes 12a, 12b to be respectively connected with the patterned capacitor electrodes 26c, 26d.